An Garda Síochána has announced that it has reopened its investigation into a 1972 bombing in Belturbet, Co Cavan, that killed two teenagers.
Citing "a number of lines of inquiry", gardaí said they have set up an incident room in nearby Ballyconnell.
Garda detectives will re-examine the events that led to the no-warning car bomb, which claimed the lives of Patrick Stanley, 16, from Clara in Offaly, and Geraldine O'Reilly, 15, from Belturbet.
The teenagers were killed instantly when the bomb exploded on the main street in the town on 28 December 1972.
The development follows a review of the case, with a senior officer now appointed to lead the investigation.
Watch on RTÉ Player:
RTÉ Investigates: Belturbet, A Bomb That Time Forgot
A loyalist group is believed to have been responsible for the bomb, but no one has ever been charged with the atrocity.
The garda review in turn followed a November 2020 investigation into the bombing by RTÉ Investigates, which identified key errors and omissions in six previous garda inquiries.
In conjunction with Professor Edward Burke, of Nottingham University, the investigation also identified "a UDA commando type gang from Belfast" who British security forces "believed [were] responsible for various explosions in Éire" at that time.
RTÉ Investigates also found that key information relevant to the bombing was not shared with gardaí by either the RUC (now the PSNI) or by British security forces.
British security files from that period, presently held by the Ministry of Defence in London, remain closed. Officially, these records will remain sealed for 84 years, which means they will not be released until 2057.
It is unclear whether information held in these British security files will be made available to the reopened garda investigation.
A number of suspects revealed by RTÉ Investigates are now deceased. Ahead of the November 2020 report, the PSNI told RTÉ Investigates that it would "provide cooperation and assistance . . . to any future investigation by An Garda Siochána".
Gardaí have appealed to anyone with information to contact them on 049 9525580.
Witnesses can also contact the Garda Confidential Line on 1800 666 111 or Crimestoppers on 1800 250 025.
Geraldine O'Reilly, who was on her Christmas holidays from school, had got a lift into Belturbet in her brother's car to buy chips.
The explosion occurred while she was in the shop, waiting to be served. She was killed instantly, with her brother Anthony seriously injured.
Ms O'Reilly's brother said it is important to get justice for his sister and Patrick Stanley, but that "time is running out".
Anthony O'Reilly welcomed the news of the reopened garda investigation.
"Its great they're investigating it. After 50 years, something might come out of it," he said.
"Some people might know something they didn't think was important at the time. After all the years, seeing it on the TV or in the news, might trigger something."
Mr O'Reilly said that "time is running out now" and that "a lot of people are passing away". He urged anyone with information to come forward.
"If they could at all, let the gardaí know, let the incident room in Ballyconnell know.
"If they know any little thing at all, that might seem important, that would bring someone to justice.
"There was a murder committed, somebody has to be responsible," he said.
Anthony himself was injured in the explosion.
He said he always thinks of what would have happened if they had not been there that night.
"It's always in the back of your mind, what their lives would have been like; Growing up, having their own families.
"The way things happen, you'd kind of be blaming yourself," he said.
Paddy Stanley was also on his Christmas holidays from school in Clara, Co Offaly. He had taken a holiday job as a helper on a Calor gas delivery lorry.
While making a delivery in Belturbet, there was a problem with the lorry and the driver decided they should stay in the town overnight.
When the bomb exploded, Paddy was in the public phone kiosk on the main street, trying to telephone his parents to tell them he would not be home. He, too, was killed instantly.
Margaret Urwin, a spokesperson for Justice for the Forgotten, said: "Together with the O'Reilly and Stanley families, we welcome whole-heartedly the decision … to initiate a new investigation.
"We have supported the two families for almost 20 years and, at last, we have this very significant and positive development in the case."